US7165456B2 - Measuring method to determine the noise emission of an electric motor and measuring device - Google Patents

Measuring method to determine the noise emission of an electric motor and measuring device Download PDF

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Publication number
US7165456B2
US7165456B2 US10/976,700 US97670004A US7165456B2 US 7165456 B2 US7165456 B2 US 7165456B2 US 97670004 A US97670004 A US 97670004A US 7165456 B2 US7165456 B2 US 7165456B2
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electric motor
measuring method
vibrational excitation
determined
noise level
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US20050092090A1 (en
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Guido Schmid
Eduard Hudec
Hubert Hauser
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Minebea Co Ltd
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Minebea Co Ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
    • G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
    • G01H1/00—Measuring characteristics of vibrations in solids by using direct conduction to the detector
    • G01H1/003—Measuring characteristics of vibrations in solids by using direct conduction to the detector of rotating machines

Definitions

  • the invention relates to a measuring method to determine the noise emission of an electric motor.
  • the invention relates further to a device to measure the noise level of an electric motor which can be used in particular to carry out the method according to the invention.
  • a measuring method to determine the noise emission of an electric motor is provided which allows the sound pressure to be ascertained in a simple and precise manner.
  • vibrational excitation of an electric motor is measured by a laser vibrometer device while the electric motor is running, and the measured vibrational excitation is correlated with a noise level.
  • the laser beam that is applied to the electric motor to be tested does not influence the resonance characteristics of the electric motor. This allows the vibrational excitation to be measured with high reproducibility which in turn allows good correlation with the noise level, i.e. the sound pressure, to be achieved. In particular, there is no need to clamp the test electric motor so that the vibrational behavior of the test electric motor is only slightly influenced by the test electric motor being supported in the respective measuring device.
  • the test electric motor can be easily positioned with respect to the laser vibrometer device.
  • the vibration amplitudes of the test electric motor measured by means of the laser vibrometer device can be analyzed and the noise level can be determined using correlation parameters.
  • this correlation it is possible to perform this correlation either for an overall noise level or for individual frequency components in the sound frequency spectrum of the test electric motor.
  • the test electric motor can be systematically scanned by means of the laser beam produced by the laser vibrometer device.
  • the vibrational excitation can be measured at that point or at those points where there is a good correlation to the sound level.
  • a laser vibrometer device ascertains the vibration amplitude of a measured object based on the Doppler effect which results in a frequency shift between the laser light which is applied to the measured object and the laser light which is reflected by the measured object.
  • a laser vibrometer device is described, for example, in DE 195 22 272 A1.
  • the vibrational excitation produced at the electric motor's nominal speed is measured, making it possible to establish a comparison with a specification.
  • the vibrational excitation is measured at one or more defined points on the electric motor. It has been demonstrated on a large number of different types of electric motors that a single measuring point is sufficient to enable the noise level to be determined using the vibrational excitation, the vibration amplitudes in turn being measured by means of the laser vibrometer device. Since only this defined measuring point need now be scanned by the laser beam, the noise emission of the test electric motor can be speedily measured.
  • the vibrational excitation is measured at one or more measuring points on the electric motor at which a vibration antinode can be formed.
  • the vibration antinode can either be an absolute amplitude maximum or a relative maximum. This measuring point is then representative for the correlation with the sound pressure, i.e. there is high correlation.
  • a surface of the electric motor(s) can be divided into a grid and the vibrational excitation to be determined by the laser vibrometer device at grid sites. This makes it possible to search systematically for a measuring point or measuring points.
  • the measuring point or measuring points is/are determined such that there is a high correlation to the noise level.
  • identically constructed electric motors are used that have a known noise level which has been previously ascertained, for example, in a sound chamber. These electric motors are then scanned and the correlation parameters to the noise level are determined. A search is then made for that point or those points which show the highest correlation. These points in turn then define the measuring point or the measuring points. These points are then established accordingly and the test electric motor and the laser vibrometer device are positioned with respect to each other in such a way that during testing the laser beam is aimed directly at the defined measuring point.
  • the measuring point or the measuring points is/are determined in the course of an octave analysis of the vibrational excitation.
  • the frequency spectrum is determined, for example, and from this frequency spectrum only the higher octave components, such as the third octave components or higher, are used in determining the measuring point or measuring points. This makes it possible to exclude low-frequency components, which can be attributed, for example, to imbalance or switching noise, when the measuring point or measuring points is/are determined.
  • the vibrational excitation for a series of identically constructed electric motors having a known noise level is determined. If a sufficiently large number of identically constructed electric motors has been chosen, high statistical reliability can be achieved in determining the correlation parameters. This in turn enables the sound pressure to be ascertained with high reproducibility once the vibration amplitude has been determined.
  • the electric motors are particularly chosen in such a way that their noise level lies within a specific noise level range.
  • This noise level range preferably comprises the range of at least twice the standard deviation. It has been proven in practice to be advantageous if this range is a four sigma range, i.e. comprises four times the standard deviation. Since then an insufficient choice of different sound pressures is available, there should also be an appropriate value range for vibration amplitudes. This in turn makes it possible to determine correlation parameters and, in particular, a correlation line (regression line) with high correlation.
  • a measuring point or several defined measuring points is/are also determined at which the test electric motors are then measured.
  • a frequency spectrum of the vibrational excitation is determined, which can be carried out, for example, using fast Fourier transformation of the data supplied by the laser vibrometer device.
  • the frequency spectrum is a spectrum of the vibration frequencies of the electric motor which is operated in particular at its nominal speed. A check can then also be made to determine whether the amplitudes at individual frequencies lie below a frequency-dependent threshold value.
  • the frequency spectrum is determined up to a minimum of 20 kHz in order to thus obtain a good overview.
  • An overall sound pressure can basically be determined as a well as a frequency-dependent sound pressure. A check can again be made to see if the overall sound pressure is below or above the threshold value and it can be checked whether the sound pressure for individual frequencies is below or above a frequency-dependent threshold value. Frequency-dependent threshold values are particularly provided to make it possible to check whether the test electric motor falls below or rises above appropriate threshold values.
  • test electric motor is freely supported and, in particular, if it is not clamped. No significant resonance shift or damping is thus caused by its support so that the sound pressure can be determined with high reproducibility.
  • test electric motor is supported in a vibration-damping way so that the influence of the surroundings on the vibrational excitation of the electric motor can be kept at a low level.
  • a device to measure the noise level of an electric motor is provided by means of which the noise level can be determined in a simple and reproducible way.
  • a supporting device is provided for the test electric motor in which the test electric motor can be freely supported, a laser vibrometer device is provided by means of which a vibrational excitation of the test electric motor can be determined, and an evaluation device is provided by means of which this vibrational excitation can be correlated to a noise level.
  • the device according to the invention is suitable for carrying out the method according to the invention.
  • the advantages of such a device have already been outlined in relation to the method according to the invention.
  • the supporting device is particularly formed in such a way that the test electric motor can be supported in a vibration-damping way. This allows the influence of the surroundings as it affects the resonance behavior of the test electric motors to be kept low.
  • the supporting device can comprise one or more damping elements onto which the test electric motor can be placed, i.e. on which it can be supported. In this way the electric motor can be vibrationally dampened with respect to its surroundings.
  • the laser vibrometer device can take the form of a scanning device allowing a surface of the electric motor to be scanned in order to determine the vibrational excitation at various locations.
  • a holding device can be provided in addition or as an alternative, on which the laser vibrometer device can be movably held.
  • the vibrational excitation for a test electric motor is determined only at this measuring point or at these few measuring points.
  • the laser vibrometer device is not limited to scan the electric motor.
  • a single-point laser vibrometer device is sufficient to determine the noise level. It is then only necessary to ensure that the laser beam produced by the laser vibrometer device is applied to the defined measuring point. Provision can be made for the laser vibrometer device and the supporting device for the test electric motor to move in relation to each other so that the application of the laser beam can be adjusted.
  • FIG. 1 a schematic perspective view of an embodiment of a measuring device to determine the noise emission of an electric motor
  • FIG. 2 a view from above of a test electric motor, on which a grid is superimposed in order to determine a measuring point;
  • FIG. 3 a comparison of the vibration amplitude at a defined measuring point with the sound pressure for a series of identically constructed electric motors and a correlation line (regression line) and its equation and
  • FIG. 4 a frequency spectrum at a defined measuring point for a series of electric motors.
  • An embodiment of a measuring device according to the invention to determine the noise emission of a test electric motor 10 comprises a baseplate 14 on which a holding device 16 for a laser vibrometer device 18 is arranged.
  • the laser vibrometer device 18 emits a laser beam 20 onto a surface 22 of the test electric motor 10 .
  • the back-reflected laser beam is registered by the laser vibrometer device 18 .
  • Vibrational excitation of the electric motor 10 can be quantitatively measured using the laser vibrometer device 18 ; the measurement principle is based on the Doppler effect. Laser vibrometer devices are thus also referred to as laser Doppler vibrometer devices.
  • the vibration frequency spectrum of the test electric motor 10 can be determined by the laser vibrometer device 18 at a scanned measuring point 24 .
  • the laser beam 20 which is applied to the test electric motor 10 has a typical beam width in the order of magnitude of 20 ⁇ m.
  • a laser vibrometer device for measuring vibrations is described, for example, in DE 195 22 272 A1.
  • the holding device 16 includes a holding frame 26 , extending above the baseplate 14 in a vertical direction.
  • a slide 28 carrying the laser vibrometer device 18 is seated on the holding frame 26 .
  • This slide 28 is preferably formed to be moveable, having a direction of movement 30 parallel to the plane of the baseplate 14 and a direction of movement 32 transversal to this which is also parallel to the plane of the baseplate 14 .
  • the laser beam 20 can be aimed at a defined measuring point 24 on the test electric motor 10 .
  • the laser vibrometer device 18 is a laser scanning vibrometer device by means of which a surface region can be scanned in a scanning process.
  • a single-point laser can also be used as an alternative, as explained in more detail below, the single-point laser vibrometer device being constructed and arranged in such a way that when the slide 28 is firmly fixed, the laser beam 20 that is emitted is aimed at a measuring point 24 on the test electric motor 10 that is fixed with respect to the baseplate 14 .
  • a supporting device indicated in its entirety by 34 is provided for the test electric motor 10 by means of which the test electric motor 10 can be supported in a defined position with respect to the baseplate 14 and the holding device 16 and thus also with respect to the laser vibrometer device 18 .
  • This supporting device 34 comprises a receiving portion 36 into which the test electric motor 10 can be placed without needing to be clamped.
  • the supporting device 34 together with the receiving portion 36 , is formed in such a way that the influence of the supporting system on the vibrational excitation of the electric motor 10 is minimized.
  • the test electric motor 10 is set on a damping element 38 which can be made from a rubber material for example. This damping element 38 vibrationally dampens the test electric motor 10 with respect to the supporting device 34 and thus with respect to the measuring device 12 .
  • the receiving portion 36 itself is seated on supports 40 ensuring improved vibrational damping.
  • a contacting device 42 is provided for the electrical contact of the electric motor 10 , this contacting device 42 having an electrical connecting element 44 .
  • the electrical connecting element 44 is adapted to an appropriate connecting element 46 of the test electric motor 10 .
  • the contacting device 42 is formed in such a way that the electrical connecting element 44 can be coupled to the electric motor 10 from above or from below with minimum contact to the surface 22 of the electric motor 10 .
  • the contacting device 42 comprises a lifting/rotary unit 48 which holds the electrical connecting element 44 with the appropriate connecting leads. This lifting/rotary unit can be rotated around an axis and is movable along this axis. This allows the electrical connecting element 44 to be set on the connecting element 46 of the test electric motor 10 from above.
  • the vibrational excitation is determined by the measuring device 10 at one or a few defined measuring points 24 using a laser Doppler measurement. According to the invention, this vibrational excitation is correlated with the noise emission of the test electric motor 10 . Correlation is effected using an evaluation device 50 . In order to carry out such measurement and correlation, some work has to be performed in advance to determine the measuring point 24 or the few measuring points 24 and to determine the correlation parameters.
  • a series of identically constructed electric motors whose noise emission is known is selected. Their noise level (sound pressure) is measured in a sound chamber, for example.
  • the number of electric motors is chosen in such a way that statistically relevant results can be derived from it. For example, 50 electric motors can be chosen.
  • a subset representing the actual test series is then chosen from this number of test motors, the noise level for these electric motors lying within a specific noise level range.
  • This defined noise level range is preferably statistically defined via the standard deviation from a medium noise level. For example, electric motors are chosen whose noise level lies in a range of four times the standard deviation (four sigma range). To determine the correlation lines in accordance with FIG. 3 , 20 electric motors were chosen.
  • the respective electric motors 52 are measured, as schematically shown in FIG. 2 , with the aid of a (virtual) grid 54 which is scanned, for example, by a scanning laser vibrometer device 18 . While the electric motor 52 is running, operating at its nominal speed in particular, the respective vibrational excitation is determined at grid points 56 using the laser vibrometer device.
  • Measuring points 24 are then determined at which there is a relatively high vibration amplitude, i.e. vibration antinodes are sought at which an absolute or at least a relative maximum of the vibration amplitude is formed.
  • a measuring point 24 or a few measuring points 24 at which there is a (relatively) large vibration amplitude, is/are then determined for the total number of electric motors. This measuring point 24 or the few measuring points 24 is/are then used to determine the noise emission for the test electric motor 10 .
  • the supporting device 34 and the laser vibrometer device 18 are accordingly positioned with respect to each other in such a way that the laser beam 20 is aimed at the defined measuring point 24 when the test electric motor 10 is accommodated in the receiving portion 36 .
  • a single-point laser vibrometer device 18 can be used to determine the measuring point 24 or the measuring points 24 , and a single-point laser vibrometer device 18 is used to determine the noise emission of the test electric motor 10 , or the laser vibrometer device 18 can have a scanning function which, after the measuring point 24 or the measuring points 24 has/have been determined, is turned off when the noise emission of the test electric motors 10 is being determined.
  • the vibrational excitation at the measuring point 24 (corresponding to grid point 58 ) is correlated, as schematically shown in FIG. 3 , for the series of electric motors 52 having a known noise level.
  • the vibration amplitude which has been determined by the laser vibrometer device 18 at measuring point 24 for each of the electric motors 52 , is plotted on the Y axis in dB(A).
  • the sound pressure which is known for the electric motors 52 , is plotted on the X axis in dB(A).
  • Each of the measuring points 60 corresponds to an electric motor 52 .
  • the correlation parameters (that is to say the gradient and intercept of these straight lines) are determined; these parameters can in turn be used by the evaluation device 50 in order to determine—without contact—the noise level from the vibration amplitude measured by the laser vibrometer device.
  • the correlation coefficient R 2 is then determined for each grid point for this series of electric motors 52 .
  • the identified measuring point 24 (or a number of several measuring points 24 ), at which the vibrational excitation best correlates with the noise level, is preferably found where the correlation coefficient R 2 is the largest, i.e. lies the closest to one.
  • the frequency spectrum is determined, using fast Fourier transformation for example.
  • an octave analysis is preferably provided, with the third octave being used for example. This means that low-frequency influences such as imbalance and switching noise do not exert any influence on the determination of the measuring point 24 or the few measuring points 24 .
  • the measuring point 24 or the few measuring points 24 is/are known after the correlation has been determined for a series of electric motors 52 .
  • the correlation parameters are known so that according to the invention, for an identically constructed test electric motor 10 , the vibration amplitudes measured using the laser vibrometer device 18 can be correlated with the noise level (sound pressure) at a measuring point 24 .
  • the noise emission of a test electric motor 10 can be determined without contact, a result being also quickly obtainable due to the single measuring point 24 or the few measuring points 24 .
  • This in turn allows a large number of electric motors 10 (with the same construction) to be tested simply, quickly and reproducibly.
  • FIG. 4 shows frequency spectra for various electric motors which are produced as a result of the measurement at the defined measuring point 24 .
  • the frequency spectra are determined from measurement data by means of fast Fourier transformation.
  • frequency spectrum 64 deviates strongly from the other frequency spectra.
  • the electric motor with frequency spectrum 64 has too high a level of noise emission.
  • spectra can also be identified that have a distinct amplitude at low frequencies and in particular at zero frequency. This can be attributed to the imbalance of the respective electric motor. This spectrum component is filtered out in determining the sound pressure.
  • the frequencies are acoustic frequencies.
  • the electric motor itself operates at its nominal speed.
  • electric motors can be given the specification that the sound pressure is to be less than 42 dB(A).
  • a corresponding cut-off level 66 is drawn in FIG. 3 .
  • this in turn produces a threshold value 68 for the vibration amplitude at the measuring point 24 .
  • the cut-off level 66 it is possible to determine a threshold value or a threshold value range for each individual frequency for the electric motors which meet the specification. In the same way, it is possible to determine a (minimum) threshold value curve for each individual frequency of the electric motors which do not meet the noise specification.
  • a threshold value range can again be determined for each individual frequency making it possible to determine in a simple, frequency-resolved way whether an electric motor meets or does not meet the required specifications.
  • the vibration amplitude is measured by the laser vibrometer device 18 at the determined measuring point 24 of the test electric motor 10 and the noise level is calculated using correlation parameters that have been previously determined on identically constructed electric motors. This enables not only the overall noise level to be determined, but also the noise level for the individual frequency components (prominent tone).
  • this allows the noise level to be determined without contact but with high reproducibility and high precision.
  • the resonance characteristics of the test electric motor 10 are only slightly influenced by the measurement.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Measurement Of Mechanical Vibrations Or Ultrasonic Waves (AREA)
US10/976,700 2003-11-05 2004-10-29 Measuring method to determine the noise emission of an electric motor and measuring device Expired - Fee Related US7165456B2 (en)

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DE10351698 2003-11-05
DE10351698A DE10351698A1 (de) 2003-11-05 2003-11-05 Meßverfahren zur Bestimmung der Geräuschemission eines Elektromotors und Meßvorrichtung

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Cited By (1)

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US20070277609A1 (en) * 2004-09-29 2007-12-06 Schmitz Tony L Flexure-based dynamometer for determining cutting force

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Publication number Priority date Publication date Assignee Title
US8893550B2 (en) * 2005-12-02 2014-11-25 Wayne State University Non-invasive vibro-acoustic analysis
DE102007023826A1 (de) * 2007-05-21 2008-11-27 Polytec Gmbh Verfahren und Vorrichtung zur berührungslosen Schwingungsmessung
US8899115B2 (en) * 2011-04-20 2014-12-02 United Technologies Corporation Method and system for locating a laser vibrometer during non-contact scanning
KR101741670B1 (ko) * 2015-10-22 2017-05-31 주식회사 이레테크 기기 소음 스캐닝 제어 장치
JP6418132B2 (ja) * 2015-10-27 2018-11-07 Ｊｆｅスチール株式会社 電気機器の騒音測定方法及び騒音測定装置
KR101753812B1 (ko) 2016-04-05 2017-07-04 국민대학교산학협력단 Ｄｃ 모터 소음 예측을 위한 장치 및 방법
CN110907181B (zh) * 2019-11-29 2021-04-06 阜南县特立电子有限公司 一种用于震动马达生产的自动化测试系统

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Cited By (2)

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Publication number Priority date Publication date Assignee Title
US20070277609A1 (en) * 2004-09-29 2007-12-06 Schmitz Tony L Flexure-based dynamometer for determining cutting force
US7536924B2 (en) * 2004-09-29 2009-05-26 University Of Florida Research Foundation, Inc. Flexure-based dynamometer for determining cutting force

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JP4260724B2 (ja) 2009-04-30
DE10351698A1 (de) 2005-06-30
JP2005140786A (ja) 2005-06-02
US20050092090A1 (en) 2005-05-05

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